Recently, in the field of silver halide photographic light-sensitive materials, in particular, used for photographing, those having high sensitivity as typically illustrated by ISO 1,000 films, etc. or those having high image quality and high resolving power suitable for use in small format cameras as typically illustrated by 110 sized cameras or disc cameras have been desired. This desire is growing not only in color light-sensitive materials but also in black-and-white light-sensitive materials, particularly for use in photographing.
For the purpose of increasing the sensitivity, investigations have been made on various techniques including, e.g., large-sized silver halide grains, couplers with high activities, accelerated development, etc. However, the increase in sensitivity based on large-sized silver halide grains seems to be reaching its limit, as reported by G. C. Farnell and J. B. Chanter in Journal of Photographic Science, Vol. 9, page 75 (1961). Accordingly, this technique is not expected to make much contribution in the future.
The present inventors have found that development using p-phenylenediamine-based color developing agents commonly employed is a so-called parallel-type development in which silver halide grains are developed gradually and simultaneously. Even in black-and-white development, when D-76 processing or a metol/ascorbic acid type surface developer, for example, is employed, parallel-type development is observed. In parallel-type development, the tendency that the sensitivity reaches the upper-most limit becomes particularly marked in a large-sized region as compared with the granular-type development in which silver halide grains are developed at one time from the beginning (e.g., D-76 or HI-RENDOL or RD-III for X-ray development formulation by Fuji Photo Film Co., Ltd.). It has further been found that in parallel-type development the developing speed of each emulsion grains in cases of large-sized emulsions is seriously decreased even though a latent image is formed on the surface of the silver halide grains. As a result, the sensitivity is not increased but, rather, reduced and the graininess in highly exposed areas is decreased.
For the purpose of accelerating development to increase the sensitivity, the present inventors have made extensive investigations on the incorporation of various development accelerators such as hydrazine compounds in an emulsion layer or a developer. In all development accelerators, however, these are often an associated increase in fog and deterioration in graininess. This is, the acceleration of development of large-sized grains cannot be attained without causing other problems.
In addition, investigations have been made to increase the sensitivity by using conventional couplers of high sensitivity. In this case, however, an increase in fog and deterioration in graininess seriously occur. That is, the conventional couplers fail to satisfactorily increase the sensitivity.